I really don't. I am not a lawyer. I can see what it asks of contributors, but I don't know when it's required, how to present it, and whether it serves its int

I really don't. I am not a lawyer. I can see what it asks of contributors, but I don't know when it's required, how to present it, and whether it serves its intended purpose. Some licenses (e.g. Apache-2.0) have some language about this built in. Some don't. When would I use this?